Objectives and problems to be solved: The main objectives of the R&D project COMHUB are the development and design of an innovative light-weight rotor hub made of composite materials, it's manufacturing and the monitoring of the performance of a first prototype. The prototype hub will be installed on a standard medium-range three-bladed pitch-controlled wind turbine in a high wind site. Specific objectives of the project are:· Design of a composite hub with a 50% weight reduction compared to nowadays cast iron hubs· Manufacturing of a prototype hub with innovative production technology (Resin Injection Moulding)· Experimental measurements on the composite hub installed on a wind turbine for one month aiming to a comprehensive monitoring and technical evaluation of the composite hub. · Experimental analysis of thick laminates under static loading and under unit-axial fatigue loading.· Standardisation of the design of composite hubs· Preliminary economical evaluation of energy production costs. · Reduction of specific component manufacturing costs up to 20% compared to current technology. Description of the work: The consortium has adapted the following approach: · Definition of constraints for the composite hub design from the wind turbine and rotor blades. Besides load and geometry aspects, constraints should consider the standardisation of hub flanges in order to ensure the adaptability to standard blades· Design of the hub with Finite Element software codes. Mayor issue is the modelling and data analysis of thick shell composite materials and the fracture analysis. The service life of the hub will be calculated first with simulated load time series and second with loads given as Markov-matrices. · Consideration of new design constraints, such as weight, angular stiffness, material damping.· Implementation of specific fracture criteria for fibre and inter laminar failure into the design algorithm.· Development of new technologies for joining composite-composite and composite-steel parts. · Analysis of rotor dynamics with the composite hub and blades taking into account stiffness and material damping in order to avoid any undesired resonance situation of the rotor and the wind turbine.· Experimental characterisation of composite materials properties (rigidity, strength and fatigue) under standard axial-axial loading in static and fatigue.· Manufacturing of a prototype of composite hub with about 4 m diameter based on advanced production technologies.· Assessment of the static mechanical performance of the composite hub during 1 month of monitoring on a high wind site. The composite hub will be tested in-site on a standard pitch-controlled wind turbine in order to validate finite element calculations and to guarantee the correct static performance of the hub.· Preliminary study of the economic viability of the composite hub by taking into account the costs of manufacture, energy production and market penetration aspects. Expected results and exploitation plans: Wind turbine components should be produced in mass series and with a low specific weight. A good acceptance of the composite hub for wind turbines depends on their manufacturing price and technical performance compared to cast iron hubs. The monitoring of a composite hub installed on a wind turbine will enable a initial technical evaluation. Secondary positive technical effects of the composite hub are regarding the dynamic behaviour of the turbine. The definition of an innovative lightweight composite rotor system, consisting of rotor blades and hub, is essential for market penetration. The exploitation of results will be of benefit of all participants of the project in order to increase the competitiveness on the market, such as the diversification of industrial activities and the creation of engineering rules and production technology knowledge.
The project final outcome can be summarised as follows (this survey relates to the expected deliverables described above): The constraints for the design of a composite hub have been identified and stated. Those constraints come from both the rotor and the blades (D1). A complete static and fatigue characterisation of a composite material consisting of glass fibre reinforced epoxy have been achieved (D2). By means of Finite Element Method, a composite hub has been designed which obeys its mechanical and production-related requirements (D3). It has been developed a feasible way to joint a composite hub to the rotor and blades. The solution chosen consists on T-bolt joints (D4). A complete methodology for the finite element simulation of thick composite materials has been introduced in the design. This methodology accounts for both the elastic properties of the layered material as well as the fatigue behaviour under multiaxial loads. Strength analysis has been based on threshold values in strain (D5).
The composite hub design has been monitored and finally approved by a certifying institution. This fact represents a first step towards the development of standards for composite hubs (D6). The most critical areas of such a composite hub have been identified, by means of numerical methods, in order to be monitored during the testing campaign (D7). The influence of a composite hub on the rotor dynamics has been analysed (D8). A composite hub prototype has been produced. This step involved the development of improved production methodologies for a composite part with such a 3D geometry (D10). That prototype has been instrumented with strain gauges for "in situ" testing (D11). Finally, the main conclusions of the development of such a complex composite part as well as its influence on the rotor dynamics have been summarised and reported (D12) and its technical and economical feasibility evaluated (D13).
Funding SchemeCSC - Cost-sharing contracts